Thermoelectric conversion material and thermoelectric conversion module

Abstract

A thermoelectric conversion material having excellent thermoelectric performance over a wide temperature range, and a thermoelectric conversion module providing excellent junctions between thermoelectric conversion materials and electrodes. An R-T-M-X-N thermoelectric conversion material has a structure expressed by the following formula: R.sub.rT.sub.t-mM.sub.mX.sub.x-nN.sub.n (0r1, 3tm5, 0m0.5, 10x15, 0n2), where R represents three or more elements selected from the group consisting of rare earth elements, alkali metal elements, alkaline-earth metal elements, group 4 elements, and group 13 elements, T represents at least one element selected from Fe and Co, M represents at least one element selected from the group consisting of Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au, X represents at least one element selected from the group consisting of P, As, Sb, and Bi, and N represents at least one element selected from Se and Te.

Claims

1. A thermoelectric conversion module comprising: a thermoelectric conversion material; an electrode; and a joining member provided between the thermoelectric conversion material and the electrode, wherein the thermoelectric conversion material has a structure expressed by the formula: Ga.sub.0.1R.sub.r-0.1T.sub.t-mM.sub.mX.sub.x-nN.sub.n (0.1<r1, 3tm5, 0m0.5, 10x15, 0n2), where R represents two or more elements belonging to at least two different groups selected from the groups consisting of a rare earth element group, an alkaline-earth metal element group, and a group 4 element group, and the rare earth element group consists of La, Ce, Pr, and Yb, the alkaline-earth metal element group consists of Ca and Ba, and the group 4 element group consists of Ti, R optionally contains a group 13 element consisting of Al and In, T represents at least one element selected from Fe and Co, M represents at least one element selected from the group consisting of Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au, X represents Sb, and N represents at least one element selected from Se and Te, wherein either m or n in Ga.sub.0.1R.sub.r-0.1T.sub.t-mM.sub.mX.sub.x-nN.sub.n is larger than 0, and wherein said joining member is a joining layer including an alloy layer made of at least one alloy selected from the group consisting of a titanium alloy that contains 50 wt % or more and less than 100 wt % of Ti, and more than 0 wt % and 50 wt % or less of at least one element of Al, Ga, In and Sn; a cobalt alloy that contains 50 wt % or more and less than 100 wt % of Co, and more than 0 wt % and 50 wt % or less of Ti; and an iron alloy that contains 50 wt % or more and less than 100 wt % of Fe, and more than 0 wt % and 50 wt % or less of Ti.

2. The thermoelectric conversion module as claimed in claim 1, wherein a difference in thermal expansion coefficient at 20 to 600 C. between said thermoelectric conversion material and said alloy layer of said joining member located closest to said thermoelectric conversion material is equal to or larger than 0% and equal to or smaller than 20% with respect to a value of a thermal expansion coefficient of said thermoelectric conversion material.

3. The thermoelectric conversion module as claimed in claim 1, wherein said alloy layer has a thermal expansion coefficient that is equal to or greater than 810.sup.6 (/K) and equal to or smaller than 1510.sup.6 (/K) at 20 to 600 C.

4. The thermoelectric conversion module as claimed in claim 1, wherein said electrode contains an alloy selected from the group consisting of titanium alloys, nickel alloys, cobalt alloys, and iron alloys.

5. The thermoelectric conversion module as claimed in claim 1, wherein said electrode is a metal or an alloy having a thermal expansion coefficient that is equal to or greater than 810.sup.6 (/K) and equal to or smaller than 1510.sup.6 (/K) at 20 to 600 C.

6. The thermoelectric conversion module as claimed in claim 1, wherein said electrode is made of an alloy having the same composition as said alloy layer.

7. The thermoelectric conversion module as claimed in claim 1, wherein T in Ga.sub.0.1R.sub.r-0.1T.sub.t-mM.sub.mX.sub.x-nN.sub.n (0.1<r1, 3tm5, 0m0.5, 10x15, 0n2) is composed of Fe and Co.

8. The thermoelectric conversion module as claimed in claim 1, wherein R in Ga.sub.0.1R.sub.r-0.1T.sub.t-mM.sub.mX.sub.x-nN.sub.n (0.1<r1, 3tm5, 0m0.5, 10x15, 0n2) represents three or more elements belonging to at least three different groups selected from the groups consisting of the rare earth element group, the alkaline-earth metal element group, and the group 4 element group.

9. The thermoelectric conversion module as claimed in claim 1, wherein R further contains In.

10. The thermoelectric conversion module as claimed in claim 1, wherein a temperature range for use of the thermoelectric conversion material is from room temperature to 600 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and advantages of the present invention will be more apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings.

(2) FIG. 1 is a diagram showing the structure of a p/n element pair of a thermoelectric conversion module.

(3) FIG. 2 is a graph showing the temperature dependence of the Seebeck coefficients of p-type thermoelectric conversion materials.

(4) FIG. 3 is a graph showing the temperature dependence of the electric resistivities of the p-type thermoelectric conversion materials.

(5) FIG. 4 is a graph showing the temperature dependence of the electrical power factors of the p-type thermoelectric conversion materials.

(6) FIG. 5 is a graph showing the temperature dependence of the thermal conductivities of the p-type thermoelectric conversion materials.

(7) FIG. 6 is a graph showing the temperature dependence of the dimensionless figures of merit of the p-type thermoelectric conversion materials.

(8) FIG. 7 is a graph showing the temperature dependence of the Seebeck coefficients of n-type thermoelectric conversion materials.

(9) FIG. 8 is a graph showing the temperature dependence of the electric resistivities of the n-type thermoelectric conversion materials.

(10) FIG. 9 is a graph showing the temperature dependence of the electrical power factors of the n-type thermoelectric conversion materials.

(11) FIG. 10 is a graph showing the temperature dependence of the thermal conductivities of the n-type thermoelectric conversion materials.

(12) FIG. 11 is a graph showing the temperature dependence of the dimensionless figures of merit of the n-type thermoelectric conversion materials.

BEST MODE FOR CARRYING OUT THE INVENTION

(13) A certain preferred embodiment of thermoelectric conversion materials and thermoelectric conversion modules according to the present invention will now be described in detail with reference to the accompanying drawings. In the drawings, like components are denoted by like reference numerals, and the same explanation will not be repeated.

(14) A thermoelectric conversion material according to this embodiment is an R-T-M-X-N thermoelectric conversion material that has a structure expressed by the following formula: R.sub.rT.sub.tmM.sub.mX.sub.xnN.sub.n (0<r1, 3tm5, 0m0.5, 10x15, 0n2),

(15) where R represents three or more elements selected from the group consisting of rare earth elements, alkali metal elements, alkaline-earth metal elements, group 4 elements, and group 13 elements,

(16) T represents at least one element selected from Fe and Co,

(17) M represents at least one element selected from the group consisting of Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au,

(18) X represents at least one element selected from the group consisting of P, As, Sb, and Bi, and

(19) N represents at least one element selected from Se and Te.

(20) Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

(21) Examples of alkali metal elements include Li, Na, K, Rb, Cs, and Fr.

(22) Examples of alkaline-earth metal elements include Ca, Sr, and Ba.

(23) Examples of group 4 elements include Ti, Zr, and Hf.

(24) Examples of group 13 elements include B, Al, Ga, In, and Tl.

(25) R represents three or more elements selected from the group consisting of rare earth elements, alkali metal elements, alkaline-earth metal elements, group 4 elements, and group 13 elements, and may be elements selected from different groups or may be elements selected from the same group. Examples of R in p-type thermoelectric conversion materials include a combination of three or more elements mainly selected from rare earth elements La and Ce, group 4 elements Ti, Zr, and Hf, and group 13 elements Al, Ga, and In. Examples of R in n-type thermoelectric conversion materials include a combination of three or more elements mainly selected from a rare earth element Yb, alkaline-earth metal elements Ca, Sr, and Ba, and group 13 elements Al, Ga, and In.

(26) A thermoelectric conversion material according to this embodiment is not particularly limited, as long as it has a structure that satisfies the formula of the present invention. However, a thermoelectric conversion material according to this embodiment preferably has a filled skutterudite structure represented by the chemical formula RT.sub.4X.sub.12 (R being a metal, T being a transition metal, X being pnictogen). A thermoelectric conversion material having such a structure can be produced by a combination of a melting technique, a rapid solidification technique (gas atomization, water atomization, centrifugal atomization, a single-roll process, or a twin-roll process), a mechanical alloying technique (a ball mill technique), or a single-crystal growth technique, and a hot press technique, a heat sintering technique, a spark plasma sintering technique, or a heat treatment technique. However, the manufacture method is not limited to the above, as long as a filled skutterudite structure can be obtained.

(27) Next, specific examples (i) to (iii) of methods for synthesizing a thermoelectric conversion material according to this embodiment will be described below.

(28) (i) An example of a combination of a melting technique and a heat treatment technique is described as a method for synthesizing a thermoelectric conversion material according to this embodiment. Pure metal materials in predetermined proportions are put into a carbon crucible, and are heated to 1200 C. and melted by heating in an inert gas atmosphere with an electric furnace. After being maintained for 5 hours, they are maintained at 900 C. for 6 hours, 800 C. for 12 hours, 700 C. for 24 hours, and further 600 C. for 12 hours. After that, the materials are cooled to room temperature. In this manner, a desired thermoelectric conversion material can be obtained.

(29) (ii) An example of a combination of a melting technique and a spark plasma sintering technique is described as a method for synthesizing a thermoelectric conversion material according to this embodiment. Pure metal materials in predetermined proportions are put into a carbon crucible, and they are heated to 1200 C. and melted by heating in an inert gas atmosphere. After being maintained for 5 hours, they are rapidly cooled into water. The water quenched materials are heated to 700 C. After being maintained for 24 hours, they are cooled to room temperature to obtain a desired ingot. The ingot material is pulverized, and the obtained powders are put into a carbon die. The powders are then heated to a temperature of 500 to 750 C. in vacuum or in an inert gas atmosphere while being subjected to a pulse current under a pressure of 60 MPa. After being maintained for 10 minutes, they are cooled to room temperature. In this manner, a desired thermoelectric conversion material can be obtained.

(30) (iii) An example of a combination of a mechanical alloying technique and a spark plasma sintering technique is described as a method for synthesizing a thermoelectric conversion material according to this embodiment. First, pure metal powders in predetermined proportions are put into an alumina container in an inert gas atmosphere, and are mixed with alumina balls. Mechanical alloying is then performed for 24 hours to obtain raw powders. The powders are put into a carbon die, and are heated to a temperature of 500 to 750 C. in vacuum or in an inert gas atmosphere while being subjected to a pulse current under a pressure of 60 MPa. After being maintained for 10 minutes, the sintered materials are cooled to room temperature. In this manner, a desired thermoelectric conversion material can be obtained.

(31) In any of the cases where one of the above synthesis methods (i) to (iii) was used, powder X-ray diffraction confirmed that the obtained thermoelectric conversion material had a filled skutterudite structure. Further, the relationships among the Seebeck coefficient S, the electric resistivity , the thermal conductivity , and temperature T were measured, and the temperature dependence of the dimensionless figure of merit ZT was examined. As a result, the dimensionless figure of merit ZT became larger with an increase in temperature, and reached 1.0 to 1.3 at temperatures ranging from room temperature to 600 C.

(32) Next, referring to FIG. 1, a thermoelectric conversion module according to this embodiment is described. FIG. 1 is a schematic diagram of the structure of the pair of p/n elements of the thermoelectric conversion module according to this embodiment.

(33) As shown in FIG. 1, the thermoelectric conversion module of this embodiment includes joining members 3 between a p-type thermoelectric conversion material 1 and electrodes 4, and between an n-type thermoelectric conversion material 2 and the electrodes 4.

(34) In this embodiment, the p-type thermoelectric conversion material 1 or the n-type thermoelectric conversion material 2 is a compound that has a filled skutterudite structure.

(35) Further, the p-type thermoelectric conversion material 1 or the n-type thermoelectric conversion material 2 has a structure expressed by the following formula: R.sub.rT.sub.tmM.sub.mX.sub.xnN.sub.n (0<r1, 3tm5, 0m0.5, 10x15, 0n2),

(36) where, R represents three or more elements selected from the group consisting of rare earth elements, alkali metal elements, alkaline-earth metal elements, group 4 elements, and group 13 elements,

(37) T represents at least one element selected from Fe and Co,

(38) M represents at least one element selected from the group consisting of Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au,

(39) X represents at least one element selected from the group consisting of P, As, Sb, and Bi, and

(40) N represents at least one element selected from Se and Te.

(41) Such a filled skutterudite thermoelectric conversion material, particularly, a Sb-based filled skutterudite thermoelectric conversion material, typically has a thermal expansion coefficient that is equal to or greater than 810.sup.6 (/K) and equal to or smaller than 1510.sup.6 (/K) at 20 to 600 C.

(42) The joining members 3 function as joining members that join the p-type thermoelectric conversion material 1 and the electrodes 4, as well as the n-type thermoelectric conversion material 2 and the electrodes 4.

(43) The joining members 3 are joining layers that include alloy layers made of at least one kind of alloy selected from the group consisting of titanium alloys, nickel alloys, cobalt alloys, and iron alloys. Further, the joining members 3 may be formed with one kind of alloy layers, but may also be formed with two or more kinds of alloy layers.

(44) Examples of the materials of the alloy layers of the joining members 3 include a Ti alloy that has titanium as a main component and contains at least one of Al, Ga, In, and Sn, a NiTi alloy that has nickel as a main component and contains titanium, a CoTi alloy that has cobalt as a main component and contains titanium, and a FeTi alloy that has iron as a main component and contains titanium.

(45) The composition ratio in the alloy layers of the joining members 3 is adjusted to match the thermal expansion coefficient of the thermoelectric conversion material. The alloy layers of the joining members 3 may be alloy layers made of a titanium alloy. The alloy layers of the joining members 3 made of a titanium alloy contain 50 wt % or more and less than 100 wt % of Ti, and more than 0 wt % and 50 wt % or less of at least one of Al, Ga, In, and Sn, based on the entire titanium alloy layers. Since the joining members 3 contain Ti, diffusion of the constituents contained in the p-type thermoelectric conversion material 1, the n-type thermoelectric conversion material 2, and the electrodes 4 can be restrained.

(46) Alternatively, the alloy layers of the joining members 3 may be alloy layers made of a nickel alloy. The alloy layers of the joining members 3 made of a nickel alloy contain 50 wt % or more and less than 100 wt % of Ni, and more than 0 wt % and 50 wt % or less of Ti based on the entire nickel alloy layers. By virtue of Ni, the difference between the thermal expansion coefficient of the alloy layers of the joining members 3 and the thermal expansion coefficient of the p-type thermoelectric conversion material can be made smaller. Since the joining members 3 also contain Ti in this case, diffusion of the constituents contained in the p-type thermoelectric conversion material 1, the n-type thermoelectric conversion material 2, and the electrodes 4 can be restrained.

(47) Alternatively, the alloy layers of the joining members 3 may be alloy layers made of an iron alloy. The alloy layers of the joining members 3 made of an iron alloy contain 50 wt % or more and less than 100 wt % of Fe, and more than 0 wt % and 50 wt % or less of Ti based on the entire iron alloy layers. By virtue of Fe, the difference between the thermal expansion coefficient of the joining members 3 and the thermal expansion coefficient of the p-type thermoelectric conversion material can be made smaller. Since the joining members 3 also contain Ti in this case, diffusion of the constituents contained in the p-type thermoelectric conversion material 1, the n-type thermoelectric conversion material 2, and the electrodes 4 can be restrained.

(48) Alternatively, the alloy layers of the joining members 3 may be alloy layers made of a cobalt alloy. The alloy layers of the joining members 3 made of a cobalt alloy contain 50 wt % or more and less than 100 wt % of Co, and more than 0 wt % and 50 wt % or less of Ti based on the entire cobalt alloy layers. By virtue of Co, the difference between the thermal expansion coefficient of the alloy layers of the joining members 3 and the thermal expansion coefficient of the p-type thermoelectric conversion material can be made smaller. Since the joining members 3 also contain Ti in this case, diffusion of the constituents contained in the p-type thermoelectric conversion material 1, the n-type thermoelectric conversion material 2, and the electrodes 4 can be restrained.

(49) The alloy layers of the joining members 3 preferably have a thermal expansion coefficient that is equal to or greater than 810.sup.6 (/K) and equal to or smaller than 1510.sup.6 (/K) at 20 to 600 C. Accordingly, good junction properties can be achieved for the p-type thermoelectric conversion material 1, the n-type thermoelectric conversion material 2, and the electrodes 4.

(50) Also, the difference in thermal expansion coefficient at 20 to 600 C. between the p-type and n-type thermoelectric conversion materials 1 and 2 and the alloy layers of the joining members is preferably equal to or more than 0% and equal to or less than 20% with respect to the values of the thermoelectric conversion materials. As the difference in thermal expansion coefficient is not larger than 20%, even better junction properties can be achieved for the p-type thermoelectric conversion material 1, the n-type thermoelectric conversion material 2, and the electrodes 4.

(51) In this embodiment, the difference in thermal expansion coefficient means that the difference between the thermal expansion coefficient of either the p-type thermoelectric conversion material 1 or the n-type thermoelectric conversion material 2 and the thermal expansion coefficient of the alloy layers of the joining members 3 with respect to the thermal expansion coefficient of either the p-type thermoelectric conversion material 1 or the n-type thermoelectric conversion material 2 is equal to or more than 0% and equal to or less than 20%.

(52) The alloy layers of the joining members 3 can be produced by a known technique such as sputtering, vapor deposition, thermal spraying, or SPS (Spark Plasma Sintering).

(53) The present invention has been made based on the findings indicating that excellent adhesion properties are exhibited between a Sb-based p-type and n-type thermoelectric conversion material having a filled skutterudite structure and a titanium alloy, a nickel alloy, a cobalt alloy, or an iron alloy. The alloy layers of the joining members 3 produce a stable compound with good adhesion properties between each of the electrodes 4 and the p-type and n-type thermoelectric conversion materials land 2, and prevent elemental diffusion between each of the electrodes 4 and the p-type and n-type thermoelectric conversion materials 1 and 2. The alloy layers of the joining members 3 can also reduce thermal stress, since the value of their thermal expansion coefficient is close to the value of the thermal expansion coefficient of the p-type thermoelectric conversion material 1, the n-type thermoelectric conversion material 2, and the material of the electrodes 4. In this embodiment, by using an alloy selected from the group consisting of predetermined titanium alloys, nickel alloys, cobalt alloys, andiron alloys to appropriately match with the variation in the thermal expansion coefficient of the Sb-based p-type thermoelectric conversion material 1 and the n-type thermoelectric conversion material 2 each having a filled skutterudite structure, good junction properties can be achieved.

(54) The electrodes 4 are connected to each of the p-type thermoelectric conversion material 1 and the n-type thermoelectric conversion material 2 via the joining members 3.

(55) The material of the electrodes 4 preferably contains an alloy selected from the group consisting of titanium alloys, nickel alloys, cobalt alloys, and iron alloys. Also, an alloy having the same composition as the alloy layers of the joining members 3 is preferably used for the material of the electrodes 4. With these materials, the adhesion properties between the two can be improved.

(56) Alternatively, the material used as the material of the electrodes 4 may be a metal or an alloy having a thermal expansion coefficient that is equal to or greater than 810.sup.6 (/K) and equal to or smaller than 1510.sup.6 (/K) at 20 to 600 C.

(57) Here, the metal or the alloy is, for example, at least one element selected from the group consisting of iron, cobalt, nickel, chromium, copper, titanium, palladium, aluminum, tin, and niobium. For example, it is possible to use alloy steel such as SUS403 or SUS430 having a thermal expansion coefficient that is equal to or greater than 810.sup.6 (/K) and equal to or smaller than 1510.sup.6 (/K) at 20 to 600 C. These materials can be joined by a known technique such as sputtering, vapor deposition, thermal spraying, SPS (Spark Plasma Sintering), or fine laser welding.

(58) According to the above structure, a thermoelectric conversion module in which the p-type thermoelectric conversion material 1 and the n-type thermoelectric conversion material 2 each having a filled skutterudite structure are joined to the electrodes 4 in a stable manner can be provided. The thermoelectric conversion efficiency of the thermoelectric conversion module of this embodiment can reach 7% or higher at temperatures ranging from room temperature to 600 C.

(59) It should be noted that the present invention is not limited to the above-described embodiment, and changes, modifications, and the like designed to achieve the object of the present invention should be considered to be within the scope of the invention.

EXAMPLES

(60) Thermoelectric conversion materials and thermoelectric conversion modules according to the present invention will be described below by way of examples. Thermoelectric conversion materials and thermoelectric conversion modules according to the present invention are not limited to the following descriptions, and various changes and modifications may be made to them without departing from the scope of the invention.

(61) [Thermoelectric Conversion Materials]

(62) (Evaluation of Thermoelectric Properties)

(63) Thermoelectric conversion materials were evaluated as follows.

(64) With the use of thermoelectric property evaluation instruments (thermoelectric property evaluation system ZEM-2 and laser flash method thermal constant measuring system TC-7000H, manufactured by ULVAC-RIKO, Inc.), the Seebeck coefficient S, the electric resistivity , and the thermal conductivity of each thermoelectric conversion material were measured at temperatures ranging from room temperature to 600 C., and the dimensionless figure of merit ZT and the electrical power factor P (P=S.sup.2/) were calculated.

Examples 1 to 4

(65) In Examples 1 to 4, the following p-type thermoelectric conversion materials were used.

(66) Example 1 p-type La.sub.0.7Ba.sub.0.07Ga.sub.0.1Co.sub.1Fe.sub.3Sb.sub.12

(67) Example 2 p-type La.sub.0.7Ba.sub.0.07Ti.sub.0.1Co.sub.1Fe.sub.3Sb.sub.12

(68) Example 3 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.3Sb.sub.12

(69) Example 4 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1.2Fe.sub.2.8Sb.sub.12

(70) The method for synthesizing the p-type thermoelectric conversion materials of Examples 1 to 4 is described below.

(71) Pure metals La, Ba, Ga, Ti, Co, Fe, and Sb in predetermined proportions were put into a crucible made of carbon, and were heated to 1200 C. and melted by heating in an inert gas atmosphere with an electric furnace. After being maintained for 5 hours, they were water quenched. The water quenched materials were then heated to 700 C. After being maintained for 24 hours, they were cooled to room temperature to obtain a desired ingot. The ingot material was pulverized, and the obtained powders were put into a carbon die. They were heated to a temperature of 500 to 750 C. in vacuum or in an inert gas atmosphere while being subjected to a pulse current under a pressure of 60 MPa. After being maintained for 10 minutes, they were cooled to room temperature to obtain the desired thermoelectric conversion material.

Comparative Example 1

(72) In this comparative example, a conventional La.sub.0.7Co.sub.1Fe.sub.3Sb.sub.12 thermoelectric conversion material was used.

(73) The thermoelectric conversion material of Comparative Example 1 was synthesized as follows.

(74) Pure metals La, Co, Fe, and Sb in predetermined proportions were put into a crucible made of carbon, and were heated to 1200 C. and melted by heating in an inert gas atmosphere with an electric furnace. After being maintained for 5 hours, they were water quenched. The water quenched materials were then heated to 700 C. After being maintained for 24 hours, they were cooled to room temperature to obtain a desired ingot. The ingot material was pulverized, and the obtained powders were put into a carbon die. They were heated to 600 C. in vacuum or in an inert gas atmosphere while being subjected to a pulse current under a pressure of 60 MPa. After being maintained for 10 minutes, they were cooled to room temperature to obtain the desired thermoelectric conversion materials.

(75) With the use of the thermoelectric conversion materials synthesized according to Examples 1 to 4 and Comparative Example 1, the thermoelectric properties of each material were evaluated. FIGS. 2 to 6 show the results.

(76) FIGS. 2 to 6 show the relationships among the Seebeck coefficients S, the electric resistivities , the electrical power factors P, the thermal conductivities , and the dimensionless figures of merit ZT of the p-type thermoelectric conversion materials obtained in Examples 1 to 4.

(77) In Examples 1 to 4, the absolute values of the Seebeck coefficients S, the electric resistivities , and the dimensionless figures of merit ZT became larger as the temperature became higher. As shown in FIG. 6, these results indicate that the dimensionless figures of merit ZT of the p-type thermoelectric conversion materials of Examples 1 to 4 became larger with the rise in temperature, and the maximum values of ZT exceeded 1 in Examples 3 and 4. Particularly, in the p-type thermoelectric conversion material La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1.2Fe.sub.2.8SB.sub.12 of Example 4, the value of the dimensionless figure of merit ZT was 0.7 at 200 C., 0.9 at 300 C., and 1.0 or greater at a temperature of 350 to 550 C., and reached 1.1, which is the maximum value of ZT, at 450 C.

(78) In Comparative Example 1, on the other hand, the absolute value of the Seebeck coefficient S, the electric resistivity , and the dimensionless figure of merit ZT became larger with a rise in temperature, but the maximum value of the dimensionless figure of merit ZT was 0.5 at 500 C.

(79) Further, as shown in FIGS. 2 to 4, in the p-type thermoelectric conversion materials of Examples 1 to 4 at temperatures ranging from room temperature to 600 C., the Seebeck coefficients S were greater than that of the conventional p-type thermoelectric conversion material La.sub.0.7Co.sub.1Fe.sub.3Sb.sub.12 of Comparative Example 1, the electric resistivities were the same as or slightly greater than that of Comparative Example 1, and the electrical power factors P were much larger than that of Comparative Example 1. Meanwhile, as shown in FIG. 5, when three or more elements selected from the group consisting of a rare earth element La, an alkaline earth element Ba, a group 4 element Ti, and a group 13 element Ga were added at the same time, the thermal conductivities became as much as approximately 40% lower than that in Comparative Example 1 where only one element La was added. By virtue of the increases in electrical power factor P and the decreases in thermal conductivity, the dimensionless figures of merit ZT of the p-type thermoelectric conversion materials of Examples 1 to 4 of the present invention became much larger in the entire temperature range of room temperature to 600 C., as shown in FIG. 6. The maximum value reached 1.1, which was 1.2 times larger than 0.5 in Comparative Example 1. This proves that the arrangement of three or more kinds of elements to the R site suggested by the present invention is effective in improving the performance of thermoelectric conversion materials.

Examples 5 to 10

(80) In Examples 5 to 10, the following n-type thermoelectric conversion materials were used.

(81) Example 5 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.12

(82) Example 6 n-type Yb.sub.0.3Ca.sub.0.1Ga.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.12

(83) Example 7 n-type Yb.sub.0.3Ca.sub.0.1In.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.12

(84) Example 8 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.12

(85) Example 9 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1In.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.12

(86) Example 10 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1In.sub.0.3Co.sub.3.75Fe.sub.0.25Sb.sub.12

(87) The method for synthesizing the n-type thermoelectric conversion materials of Examples 5 to 10 is described below.

(88) Pure metals Yb, Ca, Al, Ga, In, Co, Fe, and Sb in predetermined proportions were put into a crucible made of carbon, and were heated to 1200 C. and melted by heating in an inert gas atmosphere with an electric furnace. After being maintained for 5 hours, they were maintained at 900 C. for 6 hours, 800 C. for 12 hours, 700 C. for 24 hours, and further, 600 C. for 12 hours. They were then cooled to room temperature to obtain a desired ingot. The ingot material was pulverized, and the obtained powders were put into a carbon die. They were heated to a temperature of 500 to 750 C. in vacuum or in an inert gas atmosphere while being subjected to a pulse current under a pressure of 60 MPa. After being maintained for 10 minutes, they were cooled to room temperature to obtain the desired thermoelectric conversion materials.

Comparative Example 2

(89) In this comparative example, a conventional n-type Yb.sub.0.15Co.sub.4Sb.sub.12 thermoelectric conversion material was used.

(90) The thermoelectric conversion material of Comparative Example 2 was synthesized as follows.

(91) Pure metals Yb, Co, and Sb in predetermined proportions were put into a crucible made of carbon, and were heated to 1200 C. and melted by heating in an inert gas atmosphere with an electric furnace. After being maintained for 5 hours, they were maintained at 900 C. for 6 hours, subsequently 800 C. for 12 hours, 700 C. for 24 hours, and further, 600 C. for 12 hours. They were then cooled to room temperature to obtain a desired ingot. The ingot material was pulverized, and the obtained powders were put into a carbon die. They were heated to 700 C. in vacuum or in an inert gas atmosphere while being subjected to a pulse current under a pressure of 60 MPa. After being maintained for 10 minutes, they were cooled to room temperature to obtain the desired thermoelectric conversion materials.

(92) With the use of the thermoelectric conversion materials synthesized according to Examples 5 to 10 and Comparative Example 2, the thermoelectric properties of each material were evaluated. FIGS. 7 to 11 show the results.

(93) FIGS. 7 to 11 show the relationships among the Seebeck coefficients S, the electric resistivities , the electrical power factors P, the thermal conductivities , and the dimensionless figures of merit ZT of the n-type thermoelectric conversion materials obtained in Examples 5 to 10.

(94) In Examples 5 to 10, the absolute values of the Seebeck coefficients S, the electric resistivities , and the dimensionless figures of merit ZT became larger as the temperature became higher, and the maximum values of ZT reached 1.0 to 1.3. As can be seen from FIG. 11, in the n-type thermoelectric conversion material Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1In.sub.0.3Co.sub.3.75Fe.sub.0.25Sb.sub.12 of Example 10, the dimensionless figure of merit ZT was 0.8 at 200 C., was larger than 1 at temperatures ranging from 300 to 600 C., and was 1.3 at 550 C. It has become apparent that the value of the dimensionless figure of merit ZT of this n-type thermoelectric conversion material exceeds 1 at a wide range of temperatures of 300 to 600 C., and this n-type thermoelectric conversion material has excellent thermoelectric properties at temperatures ranging from room temperature to 600 C.

(95) In Comparative Example 2, on the other hand, the dimensionless figure of merit ZT was 0.5 at 200 C., and was 0.6 at 300 C. The maximum value of the dimensionless figure of merit ZT was 0.7 at temperatures ranging from 400 to 600 C.

(96) Comparisons among Examples 5 to 10 and Comparative Example 2 show that the addition of multiple elements Al, Ga, In, Yb, and Ca adversely affected the absolute value of the Seebeck coefficient and the electric resistivity of each material, and reduced the value of each electrical power factor P. On the other hand, the addition of the multiple elements greatly reduced the thermal conductivities of the thermoelectric conversion materials of Examples 5 to 10, and the values of the thermal conductivities became as small as half the thermal conductivity of the n-type thermoelectric conversion material Yb.sub.0.15Co.sub.4Sb.sub.12 of Comparative Example 2. Accordingly, the dimensionless figures of merit ZT of the n-type thermoelectric conversion materials of Examples 5 to 10 increased from 0.7, which is the maximum value of Comparative Example 2, to 1.0 to 1.3. This proves that the simultaneous existence of three or more kinds of elements at the R site suggested by the present invention is effective particularly in improving the performance of thermoelectric conversion materials.

Examples 11 to 20

(97) Table 1 shows the compositions of thermoelectric conversion materials of Examples 11 to 20, and the results of evaluations made on the thermoelectric properties of the respective thermoelectric conversion materials.

(98) The above-described method for synthesizing the p-type thermoelectric conversion materials was used in Examples 11 to 15 and the above-described method for synthesizing the n-type thermoelectric conversion materials was used in Examples 16 to 20 to synthesize the thermoelectric conversion materials having the respective compositions, and the thermoelectric properties of the respective materials were evaluated.

(99) TABLE-US-00001 TABLE 1 Maximum value Example Composition of ZT 3 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.3Sb.sub.12 1.00 11 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.2.9Ru.sub.0.1Sb.sub.12 1.03 12 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.2.9Rh.sub.0.1Sb.sub.12 1.05 13 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.2.9Pt.sub.0.1Sb.sub.12 1.05 14 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.3Sb.sub.11.5Te.sub.0.5 1.04 15 p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.3Sb.sub.11.5Se.sub.0.5 1.05 8 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.12 1.10 16 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.7Fe.sub.0.2Os.sub.0.1Sb.sub.12 1.15 17 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.7Fe.sub.0.2Ir.sub.0.1Sb.sub.12 1.14 18 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.7Fe.sub.0.2Pd.sub.0.1Sb.sub.12 1.13 19 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.11.5Te.sub.0.5 1.15 20 n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.11.5Se.sub.0.5 1.14

(100) As a result of partially substituting Fe in the p-type La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Co.sub.1Fe.sub.3Sb.sub.12 thermoelectric conversion material of Example 3 by Ru, Rh, and Pt, the thermal conductivities of the p-type thermoelectric conversion materials of Examples 11 to 13 became lower than the thermal conductivity of Example 3. Accordingly, the maximum value of the dimensionless figure of merit ZT indicating the thermoelectric characteristics became larger than 1.0, which was the maximum value of the dimensionless figure of merit ZT of Example 3, and reached 1.03 to 1.05. Further, as a result of partially substituting Sb by Te and Se, the electric resistivities of the p-type thermoelectric conversion materials of Examples 14 and 15 became lower than the electric resistivity of Example 3. Accordingly, the maximum value of the dimensionless figure of merit ZT indicating the thermoelectric characteristics became larger than 1.0, which was the maximum value of the dimensionless figure of merit ZT of Example 3, and reached 1.04 to 1.05.

(101) As a result of partially substituting Fe in the n-type Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Co.sub.3.75Fe.sub.0.25Sb.sub.12 thermoelectric conversion material of Example 8 by Os, Ir, and Pd, the thermal conductivities of the n-type thermoelectric conversion materials of Examples 16 to 18 became lower than the thermal conductivity of Example 8. Accordingly, the maximum value of the dimensionless figure of merit ZT indicating the thermoelectric characteristics became larger than 1.1, which was the maximum value of the dimensionless figure of merit ZT of Example 8, and reached 1.13 to 1.15. Further, as a result of partially substituting Sb by Te and Se, the electric resistivities of the n-type thermoelectric conversion materials of Examples 19 and 20 became lower than the electric resistivity of Example 8. Accordingly, the maximum value of the dimensionless figure of merit ZT indicating the thermoelectric characteristics became larger than 1.1, which was the maximum value of the dimensionless figure of merit ZT of Example 8, and reached 1.14 to 1.15.

(102) These results prove that the thermal conductivity can be further lowered and the value of the dimensionless figure of merit ZT can be made larger by substituting at least part of an element Fe or an element Co by at least one element selected from the group consisting of elements Ru, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au. Furthermore, these results prove that the value of the electrical power factor P can be made larger and the value of the dimensionless figure of merit ZT can be made even larger by substituting at least part of elements P and As or an element Sb by at least one element selected from the group consisting of elements Se and Te.

(103) [Thermoelectric Conversion Module]

(104) In the following, thermoelectric conversion modules according to the present invention will be specifically described by way of Examples.

Example 21

(105) A p-type thermoelectric conversion material La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Fe.sub.3Co.sub.1Sb.sub.12 (having a thermal expansion coefficient of approximately 13.510.sup.6 (/K) at 20 to 600 C.) and an n-type thermoelectric conversion material Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1Fe.sub.0.25Co.sub.3.75Sb.sub.12 (having a thermal expansion coefficient of approximately 10.510.sup.6 (/K) at 20 to 600 C.) were both cut and processed into prismatic columns of 5 mm5 mm7 mm by a diamond cutter. Eighteen prismatic p-elements and eighteen prismatic n-elements were used, and the eighteen pairs of p/n elements were arranged in a 40-mm-square area. Using Ni.sub.3Ti (79 wt % of Ni, 21 wt % of Ti) having a thermal expansion coefficient of 12.210.sup.6 (/K) at 20 to 600 C. as the joining members and the electrode members, a thermal spraying operation was performed to electrically series-connect both ends of each p/n element, to produce eighteen pairs of 40-mm-square thermoelectric conversion modules.

(106) A heat cycle test was conducted on the thermoelectric conversion modules manufactured by the above method. Specifically, a heat cycle test was conducted in an argon atmosphere, by using a block heater on the hot side, and performing air cooling by a fan and a heat sink on the cold side. The temperature of the hot side electrodes was increased from 200 C. to 600 C. in 30 minutes, and was maintained for 2 hours. Then, the temperature of the hot side electrodes was controlled to drop to 200 C. in 30 minutes. This cycle was repeated until the number of completed cycles reached 100 in total. As a result, there was no increase in internal resistance of the thermoelectric conversion modules measured in each cycle, and it became apparent that very good junctions were formed.

(107) After the heat cycle test, the power generation performance of the thermoelectric conversion modules were measured under the condition that the temperature of the hot side was 600 and 700 C., and the temperature of the cold side was 50 C. As a result, the respective maximum power outputs were 16 W and 21 W, and the output densities were 1.0 W/cm.sup.2 and 1.3 W/cm.sup.2.

(108) The above results indicate that the thermoelectric conversion modules manufactured with the use of the thermoelectric conversion materials and the method for manufacturing a thermoelectric conversion module according to the present invention have high durability and excellent power generation performance.

Example 22

(109) A p-type thermoelectric conversion material La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Fe.sub.2.8Co.sub.1.2Sb.sub.12 (having a thermal expansion coefficient of approximately 14.010.sup.6 (/K) at 20 to 600 C.) and an n-type thermoelectric conversion material

(110) Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1In.sub.0.1Fe.sub.0.25Co.sub.3.75Sb.sub.12 (having a thermal expansion coefficient of approximately 10.010.sup.6 (/K) at 20 to 600 C.) were both cut and processed into prismatic columns of 5 mm5 mm7 mm by a diamond cutter. Thirty-two prismatic p-elements and thirty-two prismatic n-elements were used, and the thirty-two pairs of p/n elements were arranged in a 50-mm-square area. Also, 95 wt % of Ni and 5 wt % of Ti having a thermal expansion coefficient of 13.010.sup.6 (/K) at 20 to 600 C. were used as the joining members of the p-type thermoelectric conversion material, and Ti.sub.3(Al, Sn) (80 wt % of Ti, 15 wt % of Al, 5 wt % of Sn) having a thermal expansion coefficient of 10.410.sup.6 (/K) at 20 to 600 C. was used as the alloy layers 1 of the joining members of the n-type thermoelectric material. Further, 85 wt % of Co and 15 wt % of Ti having a thermal expansion coefficient of 12.010.sup.6 (/K) at 20 to 600 C. were used as the alloy layers 2 of the joining members of the n-type thermoelectric material. The alloy layers 2 were joined onto the alloy layers 1 of the joining members of the n-type thermoelectric material. Also, SUS403 was used as the electrode material. A thermal spraying operation was performed to electrically series-connect both ends of each p/n element, to produce thirty-two pairs of 50-mm-square thermoelectric conversion modules.

(111) A heat cycle test was conducted on the thermoelectric conversion modules manufactured by the above method. Specifically, a heat cycle test was conducted in an argon atmosphere, by using a block heater on the hot side, and performing air cooling by a fan and a heat sink on the cold side. The temperature of the hot side electrodes was increased from 200 C. to 600 C. in 30 minutes, and was maintained for 2 hours. Then, the temperature of the hot side electrodes was controlled to drop to 200 C. in 30 minutes. This cycle was repeated until the number of completed cycles reached 100 in total. As a result, there was no increase in internal resistance of the thermoelectric conversion modules measured in each cycle, and it became apparent that very good junctions were formed.

(112) After the heat cycle test, the power generation performance of the thermoelectric conversion modules were measured under the condition that the temperature of the hot side was 600 and 700 C., and the temperature of the cold side was 50 C. As a result, the respective maximum power outputs were 25 W and 33 W, and the output densities were 1.0 W/cm.sup.2 and 1.3 W/cm.sup.2.

(113) The above results indicate that the thermoelectric conversion modules manufactured with the use of the thermoelectric conversion materials and the method for manufacturing a thermoelectric conversion module according to the present invention have high durability and excellent power generation performance.

Example 23

(114) A p-type thermoelectric conversion material La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Fe.sub.3Co.sub.1Sb.sub.12 (having a thermal expansion coefficient of approximately 13.510.sup.6 (/K) at 20 to 600 C.) and an n-type thermoelectric conversion material Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1In.sub.0.1Fe.sub.0.25Co.sub.3.75Sb.sub.12 (having a thermal expansion coefficient of approximately 10.010.sup.6 (/K) at 20 to 600 C.) were both cut and processed into prismatic columns of 5 mm5 mm7 mm by a diamond cutter. Thirty-two prismatic p-elements and thirty-two prismatic n-elements were used, and the thirty-two pairs of p/n elements were arranged in a 50-mm-square area. Also, 95 wt % of Co and 5 wt % of Ti having a thermal expansion coefficient of 12.810.sup.6 (/K) at 20 to 600 C. were used as the alloy layers of joining members of the p-type thermoelectric conversion material, and Ti.sub.3(Al, Sn) (80 wt % of Ti, 15 wt % of Al, 5 wt % of Sn) having a thermal expansion coefficient of 10.410.sup.6 (/K) at 20 to 600 C. was used as the alloy layers 1 of the joining members of the n-type thermoelectric material. Further, 85 wt % of Co and 15 wt % of Ti having a thermal expansion coefficient of 12.010.sup.6 (/K) at 20 to 600 C. were used as the alloy layers 2 of the joining members of the n-type thermoelectric material. The alloy layers 2 were joined onto the alloy layers 1 of the joining members of the n-type thermoelectric material. Also, SUS403 was used as the electrode material. A thermal spraying operation was performed to electrically series-connect both ends of each p/n element, to produce thirty-two pairs of 50-mm-square thermoelectric conversion modules.

(115) A heat cycle test was conducted on the thermoelectric conversion modules manufactured by the above method. Specifically, a heat cycle test was conducted in an argon atmosphere by using a block heater on the hot side, and performing air cooling by a fan and a heat sink on the cold side. The temperature of the hot side electrodes was increased from 200 C. to 600 C. in 30 minutes, and was maintained for 2 hours. Then, the temperature of the hot side electrodes was controlled to drop to 200 C. in 30 minutes. This cycle was repeated until the number of completed cycles reached 100 in total. As a result, there was no increase in internal resistance of the thermoelectric conversion modules measured in each cycle, and it became apparent that very good junctions were formed.

(116) After the heat cycle test, the power generation performance of the thermoelectric conversion modules were measured under the condition that the temperature of the hot side was 600 and 700 C., and the temperature of the cold side was 50 C. As a result, the respective maximum power outputs were 25 W and 33 W, and the output densities were 1.0 W/cm.sup.2 and 1.3 W/cm.sup.2.

(117) The above results indicate that the thermoelectric conversion modules manufactured with the use of the thermoelectric conversion materials and the method for manufacturing a thermoelectric conversion module according to the present invention have high durability and excellent power generation performance.

Example 24

(118) A p-type thermoelectric conversion material La.sub.0.7Ba.sub.0.01Ga.sub.0.1Ti.sub.0.1Fe.sub.3Co.sub.1Sb.sub.12 (having a thermal expansion coefficient of approximately 13.510.sup.6 (/K) at 20 to 600 C.) and an n-type thermoelectric conversion material Yb.sub.0.3Ca.sub.0.1Al.sub.0.1Ga.sub.0.1In.sub.0.1Fe.sub.0.25Co.sub.3.75Sb.sub.12 (having a thermal expansion coefficient of approximately 10.010.sup.6 (/K) at 20 to 600 C.) were both cut and processed into prismatic columns of 5 mm5 mm7 mm by a diamond cutter. Thirty-two prismatic p-elements and thirty-two prismatic n-elements were used, and the thirty-two pairs of p/n elements were arranged in a 50-mm-square area. Also, 95 wt % of Fe and 5 wt % of Ti having a thermal expansion coefficient of 12.510.sup.6 (/K) at 20 to 600 C. were used as the alloy layers of joining members of the p-type thermoelectric conversion material, and Ti.sub.3(Al, Sn) (80 wt % of Ti, 15 wt % of Al, 5 wt % of Sn) having a thermal expansion coefficient of 10.410.sup.6 (/K) at 20 to 600 C. was used as the alloy layers 1 of the joining members of the n-type thermoelectric material. Further, 85 wt % of Co and 15 wt % of Ti having a thermal expansion coefficient of 12.010.sup.6 (/K) at 20 to 600 C. were used as the alloy layers 2 of the joining members of the n-type thermoelectric material. The alloy layers 2 were joined onto the alloy layers 1 of the joining members of the n-type thermoelectric material. Also, SUS403 was used as the electrode material. A thermal spraying operation was performed to electrically series-connect both ends of the p/n elements, to produce thirty-two pairs of 50-mm-square thermoelectric conversion modules.

(119) A heat cycle test was conducted on the thermoelectric conversion modules manufactured by the above method. Specifically, a heat cycle test was conducted in an argon atmosphere by using a block heater on the hot side, and performing air cooling by a fan and a heat sink on the cold side. The temperature of the hot side electrodes was increased from 200 C. to 600 C. in 30 minutes, and was maintained for 2 hours. Then, the temperature of the hot side electrodes was controlled to drop to 200 C. in 30 minutes. This cycle was repeated until the number of completed cycles reached 100 in total. As a result, there was no increase in internal resistance of the thermoelectric conversion modules measured in each cycle, and it became apparent that very good junctions were formed.

(120) After the heat cycle test, the power generation performance of the thermoelectric conversion modules were measured under the condition that the temperature of the hot side was 600 and 700 C., and the temperature of the cold side was 50 C. As a result, the respective maximum power outputs were 25 W and 33 W, and the output densities were 1.0 W/cm.sup.2 and 1.3 W/cm.sup.2.

(121) The above results indicate that the thermoelectric conversion modules manufactured with the use of the thermoelectric conversion materials and the method for manufacturing a thermoelectric conversion module according to the present invention have high durability and excellent power generation performance.

Comparative Example 3

(122) In the process of manufacturing the thermoelectric conversion modules of Example 22, the joining members were replaced with those made of Ti, and modules were produced under the same conditions as those in Example 22. However, the electrode material could not be joined to the p/n thermoelectric conversion materials, and modules could not be formed.

Comparative Example 4

(123) In the process of manufacturing the thermoelectric conversion modules of Example 23, the joining members were replaced with those made of Ti, and modules were produced under the same conditions as those in Example 23. However, the electrode material could not be joined to the p/n thermoelectric conversion materials, and modules could not be formed.

(124) Comparative Examples 3 and 4 prove that the Ti layer disclosed in Patent Document 3 (Japanese Laid-Open Patent Publication No. 2003-309294) is not suitable for the thermoelectric conversion materials of the present invention.

(125) This application claims the benefit of priority of Japanese Patent Application No. 2008-12213, filed on Jan. 23, 2008, and Japanese Patent Application No. 2008-64358, filed on Mar. 13, 2008, the entire disclosures of which are incorporated herein by reference.